Solvent-free crystallization for fractionation of virgin coconut oil: Effect of process conditions on kinetics and crystal properties.

This research was aimed to conduct solvent-free crystallization and fractionation of
virgin coconut oil (VCO). This study investigated the effect of surface contact areato-
volume ratio and mixing conditions on crystal characteristics. Commercially available
VCO samples, extracted by different methods, were analyzed for fatty acid and
triacylglycerol composition using GC–MS and UPLC–ELSD. VCO extracted through
enzyme and chilling–thawing cycles exhibited higher medium chain fatty acids and
medium chain triacylglycerols, which was selected for crystallization studies. Isothermal
crystallization of VCO at 21�C assessed the effect of scale of crystallizer tube on
cooling rate using Newton's law of cooling equation. The smaller tube (20 mm diameter)
with a higher surface contact area-to-volume ratio produced 4.1-fold faster cooling
and a higher crystallization yield (44%) compared to the 80 mm diameter tube
when no agitation was applied. Whereas mixing with a magnetic stirrer produced a
large number of nuclei, generating intense crystallization heat, and rendering the crystals
inseparable from liquid fraction. The process of VCO crystallization was also studied
for kinetics and crystal growth mechanism using the Avrami model employing
angled rotation of sample tube during non-isothermal crystallization. Angled rotary
mixing produced stable crystals and significantly increased the crystallization rate
(t1/2 = 26.86 min) with polyhedral or spherulitic crystal growth (n = 3.25) compared
to non-mixing condition (t1/2 = 161.87 min) with restricted linear growth (n = 1.64).
DSC analysis of VCO and its fractions obtained after crystallization using the 20 mm
tube with angled rotary mixing indicated shifts in their thermogram peaks, suggesting
differences in triacylglycerol compositions.